The invention is based on a method for the sterilization of packaging material or packaging apparatus.
For example, in a method known from German Patent Application Nos. DE-A 2 839 543 and DE-A 2 919 015, packaging containers, such as yogurt cups, made of molded thermosetting plastic are treated with a mixture of water vapor and air. In order to attain sufficient sterility, the cups must be heated to a temperature of at least 140.degree. C. To this end, the mixture comprises saturated vapor at a temperature of 138.degree. C. and air, and before use the mixture is heated to a temperature of from 250.degree. to 275.degree. C.
As a result of the additional heating of the mixture, this known method is substantially a dry-heat sterilizing method and works similarly to other known methods using superheated water vapor, hot gas or hot air. These known sterilizing methods do not take into account the long-known fact that microorganisms and spores have less resistance in moist heat than in dry heat. Sterilizing methods have therefore also been developed which use saturated vapor at a pressure in excess of atmospheric pressure (German Patent Application Nos. DE-A 2 519 329 and 3 031 084). These known methods have the disadvantage, however, that the packaging containers or materials to be sterilized must be treated in pressure-proof containers, which are relatively expensive and complicated to handle.
A further sterilizing method is also known in which the containers are treated with flowing water vapor at atmospheric pressure (German Patent Application No. DE-A 3 044 061). This method has the disadvantage that in packaging materials which include a layer of cardboard, moisture can get into the cut edges. The cardboard acts like a sponge, making the packaging material soft and causing difficulties in the subsequent heat-sealing operation.
Finally, in order to prevent infections from being transmitted from packaging machine apparatus and peripheral equipment to the packaging material or the packaged product, German Patent Application No. DE-A 1 642 069 teaches the sterilization of pouring and dispensing spaces, lines, valves, filters and similar parts of a packaging machine with which either the product or the surrounding air comes into contact by the use of saturated vapor at 125.degree. C. and 2.5 bar of superatmospheric pressure before the packaging machine is put into operation. To attain a sufficient degree of sterility, this treatment is performed for a period lasting several minutes. The disadvantage here is that to accomplish this, the various parts of the equipment must be designed to withstand the superatmospheric pressure. If alternatively hot steam is used at atmospheric pressure, then much higher temperatures and/or much longer treatment periods are necessary.
Packaging materials made of plastic that have already been introduced into the packaging machines cannot tolerate such high temperature stresses over a relatively long period. They soften and stick to parts of the machine, preventing the starting of the machine. Steam condensate also stops up the air sterilizing filter (known as an HOSCH filter) that is disposed in packaging machines in order to maintain a sterile atmosphere.
A thermal sterilizing method accordingly is needed in which the thermal stress on the parts to be sterilized, in particular packaging material and sterilizer high-capacity filters, is low and which can be performed within a short period of time.